Electrical brush and connector assembly



March 9, 1965 K. R. MATz 3,173,047

ELEcTRmAL BRUSH AND CONNECTOR ASSEMBLY Filed Aug. :51, 1962 INVENTOR. KENNETH RMATZ A T TOR/VEV United States Patent O 3,173,047 ELECTRICAIJ BRUSH AND CGNNECTGR ASEMBLY Kenneth R. Matz, Fairview Park, Ohio, assigner to Union Carbide Corporation, a corporation of New York Fired Aug. s1, 1962, ser. Nn. 220,707 4 Claims. (Cl. S10- 249) The invention relates to an electrical brush assembly comprising one or more brush bodies and at least two shunts attached thereto, and refers in particular to a construction which substantially equalizes the current ilow in different parts of the brush body or bodies.

Many electrical brush assemblies in current use comprise brush units having irregular shapes. As used herein, the term brush assembly refers to a construction comprising a brush body, or bodies in juxtaposition and the shunts electrically attached thereto, and the term brush unit refers only to the brush body or bodies constituting the brush assembly.

One brush unit in common usage, for example, comprises a brush body having a non-working surface, i.e., the surface usually opposite the face which abuts the commutator, consisting of two parallel, substantially planar surface in different planes with a step therebetween to complete the surface. The brush body is so shaped in order to t into a brush holder along with a similar brush body and accept pressure from a separate spring linger on each brush body. Another o the brush units having an irregular shape comprises two brush bodies of unequal length disposed side by side which operate in a position angular to the tangent of a commutator in an electrical machine.

Electrical leads or shunts are usually attached to the brush unit by drilling or forming small holes in a nonworking surface, inserting an end of a shunt in each hole, and cementing the shunts in place. Although the resutant construction may operate quite well when each brush body is rectangular and adjacent brush bodies are equal in length, the operating characteristics of prior art brush assemblies which comprise irregular brush units are not as good as desired. In particular, wattage losses as heat, temperature differences within a brush unit, and the cycling magnitude between adjacent brush bodies are relatively large. In addition, the working faces of the brush units frequently wear unevenly.

The primary object of the invention, therefore, is to provide an improved electrical brush assembly of the type which employs a brush unit of irregular shape.

Another object of the invention is to provide a novel construction of an electrical brush assembly which employs a brush unit of irregular shape, which construction minimizes the wattage losses as heat, reduces the current cycling magnitude between adjacent brush bodies, and improves the wear pattern of the Working tace of the assembly.

In the drawing:

FIG. 1 is a sectional view of a brush assembly made in accordance with the invention; and

FIG. 2 is a sectional view of another embodiment of the invention.

Broadly, the above objects are achieved by an elec* trical brush assembly comprising a brush unit and at least two shunts electrically attached to the unit, each of the shunts being attached at a distance from the working face of the unit which ettects substantially equal impedances between each shunt and the working face. Such a construction reduces sparking between the brush unit and the commutator during operation, and reduces overloading of one brush body or part of one brush body ordinarily having a lower impedance than the remaining 3,173,047 Patented Mar. 9, 1965 ICC parts of the unit. Thus, the temperatures throughout the brush unit tend to remain equal, and the electrical conditions at the working face are improved.

Referring now to 'the drawing, FIG. 1 shows a sectional view of a brush assembly made in accordance with the invention. As there shown, the brush assembly comprises a brush body 10 having a substantially tlat working face 12 and a non-working face 14 consisting of two parallel, planar surfaces in different planes with a step therebetween. Two holes 16 and 1S are drilled in the nonworking face 14, and two electrical shunts 20 and 22 are electrically attached to the brush body 10 by inserting each of them in one of the holes 16 and 18 and then tamping a bonding material 23, such as a copper powder, solder, or an amalgam, around them. The holes 16 and 18 are each drilled to a depth which permits a mechanically strong connection of low electrical resistance, but which also provides substantially equal distances A and B between the shunt 2t) and the working face 12 and between the shunt 22 and working tace 12 respectively. As shown in the drawing, the depths of the two holes 16 and 1S from non-working face are necessarily unequal in order to eifect the equal distances A and B. For a brush body 10 made of a uniform or symmetric composition, the impedance between each of the shunts 20 and 22 and the working face 12, in parallel directions, will be substantially equal, and the current tlow through each part ot the brush body 10 corresponding to the shunts 20 and 22 will also be substantially equal.

Another embodiment of the invention is shown in section in FIG. 2 wherein the brush assembly comprises a brush unit 29 consisting of two juxtaposed brush bodies 3h and 32 of unequal length disposed on a cylindrical communtator 34 in a position angular to thetangent of the commutator 34. The working face 36 at the bottom of the brush unit 29, which is arcuate in shape, tits flush against the commutator 34, and the non-working tace 38 at the top surface of the brush unit 29 is Hat, although it can be of any shape suitable for use in a desired brush holder. Two holes 40 and 42 are drilled in the nonworking face 38 to a depth at which the distances C and D, along parallel lines, between the bottom of each of the holes 40 and 42 and the working face 36 respectively ar substantially equal. The holes 40 and 42 are so disposed in the non-working face 38 that each of the brush bodies 30 and 32 has a hole therein. The holes 4t) and 42 are unequal in depth in order to effect equal distances C and D.

Two shunts 44 and 46 'it into the holes 40 and 42 to their bottoms respectively, and are both physically and electrically attached to the brush unit 29 by a bonding material 48 tamped around the shunts in each hole. Thus, since the brush bodies 30 and 32 are usually made of the same material or materials, the impedances between the working face 36 and the shunts 44 and 46 respectively will be substantially equal, and the current flow through the two brush bodies 30 and 32 will also be substantially equal.

In view of the foregoing description, other constructions in accordance with the invention will be apparent to those in the art. For example, the equal impedance principle described herein can be applied 'to all brush assemblies having brush units of irregular shapes and at least two shunts attached thereto. In addition, the invention can be followed no matter what type of electrical shunt connection is employed, such as rivet, spring, cement, clamp, and the like. 1t will also be apparent that when the contact and shunt connection resistances vary in different parts of a brush unit, the placement of 'the shunts in or on the brush unit may be adjusted to 3 compensate for these` different resistanees, in addition to the resistance of the brush material. In such a case, the distances between each shunt and the working face may not necessarily boequal even though substantially equal overall impedances are achieved.

The outstanding characteristicsA ofA the brush assembly of,v the invention will be appreciated-by comparing the wattage (12R) effect of it with a standardbrush assembly. For example, a standard generator brush assembly having a brush unitnominally-21/2 inches by 11/2 inches by 3A inch with a 30 angle bottom and 15 angle top Comprising two Ms inch thick brush bodies disposed side by side has a resistance of 0.003 ohm/inch of length for each brush body. The standard shunt connections are about 1.362 inches from the working face in the short brush body andabout 1.62.5 inches in the long brush body. Thus, the short brush body has a resistance of 0.0087 ohm and the long brush body 0.0104 ohm. Tests have indicated'that up to about 75 percent ofthe total current will flow through the short body and about 25 percent through the long body. Thus, the 12R loss in each body for a total current of 175 amps may be in the order of about 149.87 watts in the short body and aboutk 19.91 watts in the long body.

If the standard construction described above is modified in accordance with the invention byv placing the shunt in the long brush body at a point 1,362 inches from the working face, the current flowing through each body will be substantially equal, and the 12R loss in each will'be approximately equal rather than totally unequal as before. It has been found that the equalization of the loads in the two brush bodies causes the brush unit to operate at a more uniform temperature and wear more evenly on the working face. Furthermore, the brush assembly of the invention reduces the current cycling magnitude between brush bodies during commutation, and in general improves the stability and life of the assembly. Other advantages include a reduction in the level of sparking during commutation and a reduction in the occurrences of shunt connections becoming unsatisfactory due to high operatingtemperatures.

Whatfis claimed is:

1. Any electrical brushV assembly comprising a brush unit consisting of at least one brushbody having a bottom surface which constitutes the` working face of said unit and a top surface which constitutes 'the non-,working surface of said unit, said non-working surface being irregular in distance from said working face; andat least two shunts electrically attached tosaid brush unit; the lowest r part of one of said shunts being ay distance' from said non-working surfaceV different' fromthe corresponding distance of another of said shunts, at least one offsaid shunts being electrically attached toy each brush body by being partially'embedded and filling aohole in each' of said brush bodies, said hole extending from said nonworkingv face toward, but short of, said'working face of said brush unit, and the depth of said einbednient of said shunts being unequal, and 'these depths being such attached to said brush unit; the lowest part of one of` said shunts being a distance from said non-working surface different from the corresponding distance of another of said shunts, atleast one of said shunts being electrically attached to each of said brush bodies by being partially embedded and filling a hole in each of said brush bodies, said hole extending from said non-working face toward, but short of, said working face of said brush unit, and the depth of said einbedment of said shunts being unequal, and these depths boing such that the impedance between the different shunts and said working face of said brush unit are substantially equal.

3. An electrical brush assembly comprising a single brush body having a working face and opposite said working face a non-working face, said non-working face comprising two substantially planar, parallel surfaces in different planes with a step in between to complete said non-working face, and at least two holesin said nonworking face with each of said planar surfaces having at least one of said holes therein, the depth of one of said holes being different from the depth' ofanother of said holes and the depth of each of said holes being such that the distances between the bottom of each of said holes and said working face are substantially equal; and at least two shunts electrically attached to said unit, cach of said'shunts fitting in one of said holes to its bottoni, thus effecting substantially equal impedances between each of said shunts and' said working face.

4. An electrical brush'assembly comprising a brush unit consisting of at least two brush bodies of unequal length andhaving bottom surfaces which constitute the working face of said unit and top surfaces which constitute the non-working surface of said unit, said top surfaces having at least two holes therein with each of said top surfaces having atleast one hole, the depth of one of said holes being different from the depth of Vanother of said holes andthe depth of each of said holes being such that the distances between the bottom ofeach of said holes and said working face are substantially equal; and at least two shunts electrically attached to said unit, each of said shunts fitting in one of said holes to its bottom, thus effecting substantially equal impedances betweenveach of said' shunts and said working face.

No references cited.

l. ""QL... 

1. AN ELECTRICAL BRUSH ASSEMBLY COMPRISING A BRUSH UNIT CONSISTING OF AT LEAST ONE BRUSH BODY HAVING A BOTTOM SURFACE WHICH CONSTITUTES THE WORKING FACE OF SAID UNIT AND A TOP SURFACE WHICH CONSTITUTES THE NON-WORKING SURFACE OF SAID UNIT, SAID NON-WORKING SURFACE BEING IRREGULAR IN DISTANCE FROM SAID WORKING FACE; AND AT LEAST TWO SHUNTS ELECTRICALLY ATTACHED TO SAID BRUSH UNIT, THE LOWEST PART OF ONE OF SAID SHUNTS BEING A DISTANCE FROM SAID NON-WORKING SURFACE DIFFERENT FROM THE CORRESPONDING DISTANCE OF ANOTHER OF SAID SHUNTS, AT LEAST ONE OF SAID SHUNTS BEING ELECTRICALLY ATTACHED TO EACH BRUSH BODY BY BEING ELECTRICALLY ATTACHED TO EACH BRUSH BODY SAID BRUSH BODIES, SAID HOLE EXTENDING FROM SAID NONWORKING FACE TOWARD, BUT SHORT OF, SAID WORKING FACE OF SAID BRUSH UNIT, AND THE DEPTH OF SAID EMBEDMENT OF SAID SHUNTS BENG UNEQUAL, AND THESE DEPTHS BEING SUCH THAT THE IMPEDANCE BETWEEN THE DIFFERENT SHUNTS, AND SAID WORKING FACE OF SAID BRUSH UNIT ARE SUBSTANTIALLY EQUAL. 